U.S. patent application number 09/887929 was filed with the patent office on 2002-05-30 for redox process for preparing emulsion polymer having low formaldehyde content.
Invention is credited to Lorah, Dennis Paul, Slone, Robert Victor.
Application Number | 20020065381 09/887929 |
Document ID | / |
Family ID | 26933816 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020065381 |
Kind Code |
A1 |
Lorah, Dennis Paul ; et
al. |
May 30, 2002 |
Redox process for preparing emulsion polymer having low
formaldehyde content
Abstract
A process for preparing an aqueous emulsion polymer including
providing at least one ethylenically unsaturated monomer and a free
radical redox initiator system under emulsion polymerization
conditions, the redox initiator system composed of t-alkyl
hydroperoxide, t-alkyl peroxide, or t-alkyl perester wherein the
t-alkyl group includes at least 5 Carbon atoms and a
non-formaldehyde-forming reducing agent; and effecting the
polymerization of at least some of the ethylenically unsaturated
monomer is provided. Also provided is a process for reducing the
residual ethylenically unsaturated monomer content of an aqueous
emulsion polymer.
Inventors: |
Lorah, Dennis Paul;
(Lansdale, PA) ; Slone, Robert Victor; (Quaker,
PA) |
Correspondence
Address: |
ROHM AND HAAS COMPANY
PATENT DEPARTMENT
100 INDEPENDENCE MALL WEST
PHILADELPHIA
PA
19106-2399
US
|
Family ID: |
26933816 |
Appl. No.: |
09/887929 |
Filed: |
June 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60240904 |
Oct 17, 2000 |
|
|
|
Current U.S.
Class: |
526/222 ;
526/227; 526/234 |
Current CPC
Class: |
C08F 4/40 20130101 |
Class at
Publication: |
526/222 ;
526/227; 526/234 |
International
Class: |
C08F 004/40 |
Claims
What is claimed is:
1. A process for preparing an aqueous emulsion polymer comprising
providing at least one ethylenically unsaturated monomer and a free
radical redox initiator system under emulsion polymerization
conditions, said redox initiator system consisting essentially of
t-alkyl hydroperoxide, t-alkyl peroxide, or t-alkyl perester
wherein the t-alkyl group includes at least 5 Carbon atoms and a
non-formaldehyde-forming reducing agent; and effecting the
polymerization of at least some of said ethylenically unsaturated
monomer.
2. The process of claim 1 wherein said redox initiator system
further comprises a redox reaction catalyzing metal salt and,
optionally, a metal complexing agent.
3. The process of claim 1 wherein said non-formaldehyde-forming
reducing agent is selected from the group consisting of isoascorbic
acid, sodium metabisulfite, sodium bisulfite, sodium dithionite,
and sodium 2-hydroxy-2- sulfinatoacetic acid.
4. The process of claim 1 wherein the polymerization of at least
95% by weight of said ethylenically unsaturated monomer is
effected.
5. A process for reducing the residual ethylenically unsaturated
monomer content of an aqueous emulsion polymer comprising
contacting said aqueous emulsion polymer with a free radical redox
initiator system, said redox initiator system consisting
essentially of t-alkyl hydroperoxide, t-alkyl peroxide, or t-alkyl
perester wherein the t-alkyl group includes at least 5 Carbon atoms
and a non-formaldehyde-forming reducing agent; and effecting the
polymerization of at least some of said residual ethylenically
unsaturated monomer.
6. The process of claim 5 wherein said redox initiator system
further comprises a redox reaction catalyzing metal salt and,
optionally, a metal complexing agent.
7. The process of claim 5 wherein said non-formaldehyde-forming
reducing agent is selected from the group consisting of isoascorbic
acid, sodium metabisulfite, sodium bisulfite, sodium dithionite,
and sodium 2-hydroxy-2- sulfinatoacetic acid.
8. The process of claim 5 wherein the polymerization of at least
90% by weight of said residual ethylenically unsaturated monomer is
effected.
Description
[0001] This invention relates to a redox process for preparing an
emulsion polymer having low formaldehyde content. More
particularly, this invention relates to a process for preparing an
aqueous emulsion polymer including providing at least one
ethylenically unsaturated monomer and a free radical redox
initiator system under emulsion polymerization conditions, the
redox initiator system including t-alkyl hydroperoxide, t-alkyl
peroxide, or t-alkyl perester wherein the t-alkyl group includes at
least 5 Carbon atoms and a non-formaldehyde-forming reducing agent;
and effecting the polymerization of at least some of the
ethylenically unsaturated monomer. And the invention also relates
to a process for reducing the residual monomer content of an
emulsion polymer.
[0002] Redox initiator systems incliding at least one oxidizing
agent and at least one reducing agent and, optionally, a metal
promotor species are advantageously used in the emulsion
polymerization of ethylenically unsaturated monomers, particularly
if polymerization at temperatures lower than those at which
conventional thermal initiation systems provide an effective level
of free radical production such as at temperatures below 85.degree.
C. is desired. However, some oxidizing agents and some reducing
agents disadvantageously effect the formation of formaldehyde in
the emulsion polymer. For example, the commonly used reducing agent
sodium sulfoxylate formaldehyde and the commonly used oxidizing
agent t-butyl hydroperoxide may each generate formaldehyde during
emulsion polymerization in which thay are part of the initiator
system. The present invention serves to provide redox emulsion
polymerization processes which desirably lead to lowered
formaldehyde levels when compared with processes using alternative
redox initiator systems.
[0003] U.S. Pat. No. 5,540,987 discloses emulsion polymers
including certain copolymerized formaldehyde-generating
crosslinking monomers having lowered free formaldehyde content by
use of an initiator system including a hydrophobic hydroperoxide,
preferably t-butyl hydroperoxide, oxidizing agent and the specific
reducing agent, ascorbic acid. Improvements in lowering
formaldehyde content are still sought.
[0004] It has now been surprisingly found that lowered formaldehyde
levels are found in emulsion polymerization of ethylenically
unsaturated monomers when certain free radical redox initiator
systems are used under emulsion polymerization conditions, the
redox initiator systems including t-alkyl hydroperoxide, t-alkyl
peroxide, or t-alkyl perester wherein the t-alkyl group includes at
least 5 Carbon atoms and any non-formaldehyde-forming reducing
agent. An improvement is found in reducing residual monomer at the
end of a conventional emulsion polymerization as well as in an
emulsion polymerization.
[0005] In a first aspect of the present invention there is provided
a process for preparing an aqueous emulsion polymer including
providing at least one ethylenically unsaturated monomer and a free
radical redox initiator system under emulsion polymerization
conditions, the redox initiator system composed of t-alkyl
hydroperoxide, t-alkyl peroxide, or t-alkyl perester wherein the
t-alkyl group includes at least 5 Carbon atoms and a
non-formaldehyde-forming reducing agent; and effecting the
polymerization of at least some of the ethylenically unsaturated
monomer.
[0006] In a second aspect of the present invention there is
provided a process for reducing the residual ethylenically
unsaturated monomer content of an aqueous emulsion polymer
including contacting the aqueous emulsion polymer with a free
radical redox initiator system, the redox initiator system composed
of t-alkyl hydroperoxide, t-alkyl peroxide, or t-alkyl perester
wherein the t-alkyl group includes at least 5 Carbon atoms and a
non-formaldehyde-forming reducing agent; and effecting the
polymerization of at least some of the residual ethylenically
unsaturated monomer.
[0007] The process for preparing an aqueous emulsion polymer of
this invention includes providing at least one ethylenically
unsaturated monomer and a free radical redox initiator system under
emulsion polymerization conditions.
[0008] The aqueous acrylic emulsion polymer contains, as
copolymerized unit(s), at least one copolymerized
monoethylenically-unsaturated (meth)acrylic. monomer including
esters, amides, and nitrites of (meth)acrylic acid, such as, for
example, (meth)acrylic ester monomer including methyl acrylate,
ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl
acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate,
butyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl
methacrylate, aminoalkyl (meth)acrylate, N-alkyl aminoalkyl
(methacrylate), N,N-dialkyl aminoalkyl (meth)acrylate; urieido
(meth)acrylate; (meth)acrylonitrile and (meth)acrylamide; styrene
or alkyl-substituted styrenes; butadiene; vinyl acetate, vinyl
propionate, or other vinyl esters; vinyl monomers such as vinyl
chloride, vinylidene chloride, and N-vinyl pyrollidone; allyl
methacrylate, diallyl phthalate, 1,3-butylene glycol
dimethacrylate, 1,6- hexanedioldiacrylate, and divinyl benzene;
(meth)acrylic acid, crotonic acid, itaconic acid, sulfoethyl
methacrylate, phosphoethyl methacrylate, fumaric acid, maleic acid,
monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, and
maleic anhydride. The use of the term "(meth)" followed by another
term such as acrylate, acrylonitrile, or acrylamide, as used
throughout the disclosure, refers to both acrylate, acrylonitrile,
or acrylamide and methacrylate, methacrylonitrile, and
methacrylamide, respectively.
[0009] The free radical addition polymerization techniques used to
prepare the acrylic emulsion polymer of this invention are well
known in the art. Conventional surfactants may be used such as, for
example, anionic and/or nonionic emulsifiers such as, for example,
alkali metal or ammonium salts of alkyl, aryl, or alkylaryl
sulfates, sulfonates or phosphates; alkyl sulfonic acids;
sulfosuccinate salts; fatty acids; ethylenically unsaturated
surfactant monomers; and ethoxylated alcohols or phenols. The
amount of surfactant used is usually 0.1% to 6% by weight, based on
the weight of monomer.
[0010] A redox initiator system composed of t-alkyl hydroperoxide,
t-alkyl peroxide, or t-alkyl perester wherein the t-alkyl group
includes at least 5 Carbon atoms oxidizing agent and a
non-formaldehyde-forming reducing agent is used. Preferred is a
redox initiator system composed of t-amyl hydroperoxide oxidizing
agent and a non-formaldehyde-forming reducing agent At least one
non-formaldehyde-forming reducing agent such as, for example,
alkali metal and ammonium salts of sulfur-containing acids, such as
sodium sulfite, bisulfite, thiosulfate, hydrosulfite, sulfide,
hydrosulfide or dithionite, formadinesulfinic acid,
hydroxymethanesulfonic acid, acetone bisulfite, amines such as
ethanolamine, glycolic acid, glyoxylic acid hydrate, ascorbic acid,
isoascorbic acid, lactic acid, glyceric acid, malic acid,
2-hydroxy-2-sulfinatoacetic acid, tartaric acid and salts of the
preceding acids typically at a level of 0.01% to 3.0% by weight,
based on monomer weight, is used. Preferred reducing agents are
isoascorbic acid, sodium metabisulfite, and
2-hydroxy-2-sulfinatoacetic acid.
[0011] The present invention may also be practiced with mixtures of
oxidants to maintain the desired minimal formaldehyde level. These
mixtures may include tertiary-amylhydroperoxide along with hydrogen
peroxide, ammonium persulfate and the like. In certain embodiments
of the present invention, it is advantageous to choose a mixture
containing a hydrophilic oxidant and the hydrophobic oxidant
tert-amylhydroperoxide to increase the overall efficiency of the
initiator system with regard to the initiation of the full range of
hydrophilic and hydrophobic monomers.
[0012] Typically, 0.01% to 3.0% by weight, based on monomer weight,
of t-amylhydroperoxide oxidizing agent is used. Redox reaction
catalyzing metal salts of iron, copper, manganese, silver,
platinum, vanadium, nickel, chromium, palladium, or cobalt may
optionally be used, with or without metal complexing agents. The
oxidant and reductant are typically added to the reaction mixture
in separate streams, preferably concurrently with the monomer
mixture. The reaction temperature is maintained at a temperature
lower than 100 .degree. C. throughout the course of the reaction.
Preferred is a reaction temperature between 30 .degree. C. and 95
.degree. C., more preferably between 50 .degree. C. and 90 .degree.
C. The monomer mixture may be added neat or as an emulsion in
water. The monomer mixture may be added in one or more additions or
continuously, linearly or not, over the reaction period, or
combinations thereof.
[0013] Further, a chain transfer agent such as, for example,
isopropanol, halogenated compounds, n-butyl mercaptan, n-amyl
mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, alkyl
thioglycolate, mercaptopropionic acid, and alkyl mercaptoalkanoate
in an amount of 0.1 to 6.0% by weight based on monomer weight may
be used. Linear or branched C.sub.4-C.sub.22 alkyl mercaptans such
as n-dodecyl mercaptan and t-dodecyl mercaptan are preferred. Chain
transfer agent(s) may be added in one or more additions or
continuously, linearly or not, over most or all of the entire
reaction period or during limited portion(s) of the reaction period
such as, for example, in the kettle charge and in the reduction of
residual monomer stage.
[0014] However, at least some, preferably at least 40% by weight,
more preferably at least 75% by weight, most preferably at least
95% by weight, based on dry polymer weight, of the emulsion polymer
is formed using the redox initiator system composed of t-alkyl
hydroperoxide, t-alkyl peroxide, or t-alkyl perester wherein the
t-alkyl group includes at least 5 Carbon atoms and a
non-formaldehyde-forming reducing agent in the absence of any other
oxidizing agent and in the absence of any other reducing agent. The
emulsion polymerization is contemplated to include embodiments
where some of the polymer is introduced by a polymer seed, formed
in situ or not, or formed during hold periods or formed during
periods wherein the monomer feed has ended and residual monomer is
being converted to polymer.
[0015] In another aspect of the present invention the emulsion
polymer may be prepared by a multistage emulsion polymerization
process, in which at least two stages differing in composition are
polymerized in sequential fashion. Such a process usually results
in the formation of at least two mutually incompatible polymer
compositions, thereby resulting in the formation of at least two
phases within the polymer particles. Such particles are composed of
two or more phases of various geometries such as, for example,
core/shell or core/sheath particles, core/shell particles with
shell phases incompletely encapsulating the core, core/shell
particles with a multiplicity of cores, and interpenetrating
network particles. In all of these cases the majority of the
surface area of the particle will be occupied by at least one outer
phase and the interior of the particle will be occupied by at least
one inner phase. Each of the stages of the multi-staged emulsion
polymer may contain the same monomers, surfactants, chain transfer
agents, etc. as disclosed herein-above for the emulsion polymer.
The polymerization techniques used to prepare such multistage
emulsion polymers are well known in the art such as, for example,
U.S. Pat. Nos. 4,325,856; 4,654,397; and 4,814,373.
[0016] The emulsion polymer has an average particle diameter from
20 to 1000 nanometers, preferably from 70 to 300 nanometers.
Particle sizes herein are those determined using a Brookhaven Model
BI-90 particle sizer manufactured by Brookhaven Instruments
Corporation, Holtsville NY, reported as "effective diameter". Also
contemplated are multimodal particle size emulsion polymers wherein
two or more distinct particle sizes or very broad distributions are
provided as is taught in U.S. Pat. Nos. 5,340,858; 5,350,787;
5,352,720; 4,539,361; and 4,456,726.
[0017] The glass transition temperature ("Tg") of the emulsion
polymer is typically from -80.degree. C. to 140.degree. C.,
preferably from -20.degree. C. to 50.degree. C., the monomers and
amounts of the monomers selected to achieve the desired polymer Tg
range are well known in the art. Tgs used herein are those
calculated by using the Fox equation (T.G. Fox, Bull. Am. Physics
Soc., Volume 1, Issue No. 3, page 123(1956)). that is, for
calculating the Tg of a copolymer of monomers M1 and M2,
1/ Tg(calc.)=w(M1)/Tg(M1)+w(M2)/Tg(M2)
[0018] , wherein
[0019] Tg(calc.) is the glass transition temperature calculated for
the copolymer
[0020] w(M1) is the weight fraction of monomer M1 in the
copolymer
[0021] w(M2) is the weight fraction of monomer M2 in the
copolymer
[0022] Tg(M1) is the glass transition temperature of the
homopolymer of M1
[0023] Tg(M2) is the glass transition temperature of the
homopolymer of M2,
[0024] all temperatures being in .degree.K.
[0025] The glass transition temperatures of homopolymers may be
found, for example, in "Polymer Handbook", edited by J. Brandrup
and E.H. Immergut, Interscience Publishers.
[0026] In the second aspect of the present invention there is
provided a process for reducing the residual ethylenically
unsaturated monomer content of an aqueous emulsion polymer
including contacting the aqueous emulsion polymer with a free
radical redox initiator system, the redox initiator system composed
of t-alkyl hydroperoxide, t-alkyl peroxide, or t-alkyl perester
wherein the t-alkyl group includes at least 5 Carbon atoms and a
non-formaldehyde-forming reducing agent; and effecting the
polymerization of at least some of the residual ethylenically
unsaturated monomer. The emulsion polymer of this aspect includes
compositions, Tg, and particle sizes as described and exemplified
hereinabove, prepared with the redox initiator system of this
invention or any other free radical initiator means such as, for
example, by thermal initiation and photoinitiation having a
residual ethylenically unsaturated monomer content. The residual
ethylenically unsaturated monomer content will typically be less
than 5%, preferably less than 1%, by weight based on polymer
weight. The emulsion polymer is then contacted with a redox
initiator system composed of t-alkyl hydroperoxide, t-alkyl
peroxide, or t-alkyl perester wherein the t-alkyl group includes at
least 5 Carbon atoms and a non-formaldehyde-forming reducing agent,
in composition and amounts as described and exemplified herein
above and the polymerization of at least some, preferably at least
50%, more preferably at least 90%, of the residual ethylenically
unsaturated monomer is effected under conditions as described
hereinabove.
[0027] The emulsion polymer of this invention and the emulsion
polymer having reduced residual monomer of this invention may be
used in paints, paper coatings, leather coatings, adhesives,
nonwoven and paper saturants, and the like.
[0028] The following examples are presented to illustrate the
invention and the results obtained by the test procedures.
EXAMPLE 1.
Formaldehyde generation concurrent with reduction of residual
monomer.
[0029] A series of samples were prepared which consisted of a
preformed polymer seed, a known quantity of monomer, and a redox
initiator system. Free formaldehyde levels were determined using
HPLC; Residual monomer levels were determined using gas
chromatography. To each vial was added 30 g acrylic dispersion
polymer at 45% solids and 15 g distilled water. Then, 0.30 g 0.15%
ferrous sulfate solution was added followed by 0.20 g butyl
acrylate. The oxidant and reductant solutions were added
sequentially according to Table 1.1: All were shaken overnight at
room temperature. All samples then contained residual monomer
levels below 10 ppm. Formaldehyde levels are presented in Table
1.2.
1TABLE 1.1. Charge List for Latex Samples. Oxidizing Reducing
Sample Agent Amount (g) Agent Amount (g) Comp. A t-BHP 0.0386 IAA
0.0264 Comp. B t-BHP 0.0386 MBS 0.0143 Comp. C t-BHP 0.0386 SHSAA
0.0294 Comp. D t-BHP 0.0386 SSF 0.0231 1 t-AHP 0.0367 IAA 0.0264 2
t-AHP 0.0367 MBS 0.0143 3 t-AHP 0.0367 SHSAA 0.0294 Comp. E t-AHP
0.0367 SSF 0.0231 NOTES: t-BHP = t-butyl hydroperoxide, 70% aqueous
solution; t-AHP = t-amyl hydroperoxide, 83% in t-amyl alcohol; IAA
= isoascorbic acid; MBS = sodium metabisulfite; SSF = sodium
sulfoxylate formaldehyde SHSAA = sodium 2-hydroxy-2-sulfinatoacetic
acid (50% by weight)
[0030]
2TABLE 1.2. Latex Sample Formaldehyde Data. Additional Oxidizing
Reducing Formaldehyde* Formaldehyde* Sample Agent Agent (ppm) (ppm)
Acrylic 4.2 Latex Comp. A t-BHP IAA 7.7 3.5 Comp. B t-BHP NaMBS 6.5
2.3 Comp. C t-BHP SHSAA 8.9 4.7 Comp. D t-BHP SSF 89.0 84.8 1 t-AHP
IAA 4.4 0.2 2 t-AHP NaMBS 4.6 0.4 3 t-AHP SHSAA 4.7 0.5 Comp. E
t-AHP SSF 97.7 93.3 NOTES: *Free formaldehyde; data obtained by
HPLC. 0.4% BA on batch; 0.2% t-BHP on mmr; t-AHP is equimolar.
0.17% SSF on mmr; other reducing agents are equimolar. Examples 1-3
of this invention exhibit lower formaldehyde and additional
formaldehyde levels compared to those of Comparative Examples
A-E.
* * * * *